Are you sitting in one zone and just waiting for the hellgate in that area to respawn?

With the new zones, and new areas for hellgates to spawn, perhaps they are going on the logic that there are more 'overall' spawns in the world and they are appearing all over the map at a faster rate ..... and not just that each individual map that you are camping will reappear faster.

they still spawn as fast as before but they spawn on more zones now, and they don't despawn after 30 min like they used to so once they spawn in the new zones they will stay there forever so the chance that they won't spawn near caerleon is higher